1. Field of the Invention
The present invention relates to a glass fiber size applicator for continuous glass fiber forming operations.
2. Technical Considerations and Prior Art
Glass fibers are commonly formed by attenuating molten glass through orifices in a bushing. The fibers are then drawn across an applicator, which coats at least a portion of the fiber surface with a sizing composition, gathered into one or more discrete strands by gathering shoes, and wound on a winding machine into a forming package.
Typical starch-oil sizing compositions used for yarns and fabrics can include up to about 7 wt % solids while typical sizing compositions used for direct reinforcement of polymers and elastomers can include up to about 14 wt % solids. In formulating sizing compositions, there are several advantages to increasing the amount of solids in the sizing. First, with a high solids content there is less water so that the sizing will dry faster on the glass fibers. Also because of the lower water content, there will be less migration of the sizing during drying of the forming package, resulting in a more uniform loss on ignition (LOI) throughout the forming package. In addition, as the fibers pass over the gathering shoe to form the fiber strands and are thereafter positioned on the forming package by the spiral, there is less of a tendency to lose a portion of the sizing from the coated glass fibers as the solids content of the sizing composition increases. By increasing the solids content and thus increasing the viscosity of the sizing, less size is lost during processing and the size that is left on the fibers has a greater amount of sizing constituents. As used herein, the terms "high solids" or "high solids content" mean a composition having at least about 20 wt % solids content.
One typical applicator design known and used by those skilled in the art incorporates a roller that is continuously coated with the sizing material. The applicator is positioned relative to the newly formed glass fibers such that the glass fibers contact just enough of the coated roller surface to coat at least a portion of the fiber surface. Another typical applicator design uses a coated belt to apply the sizing material to the glass fibers. For additional information regarding different types of applicators, see K. Loewenstein, The Manufacturing Technology of Continuous Glass Fibres, (Third Edition 1993) at pages 165-172, which teachings are incorporated by reference.
When applying sizing to the fibers, it is important to provide a smooth uniform film on the applicator roll so that a uniform, consistent coating can be applied to the glass fibers. However, it has been found as the amount of solids in the sizing increases and the sizing viscosity decreases, it is difficult to maintain a uniform film coating on the applicator roll. This results in a nonuniform application of the sizing to the glass fibers, as well as excessive buildup of the sizing at the gathering shoe and spiral. In addition, in high solids sizing formulations that do provide a good consistent film, it has been found that the applicator tends to apply too much size to the glass fibers. This can be corrected by slowing the speed at which the applicator roll is coated with the sizing, but if the speed is too slow, there can be excessive breakage of the glass fibers, especially in applicators that use a rubber belt to apply the sizing.
WO 98/06551 discloses single and dual roll applicators having a roller positioned in a pan supplied with the sizing composition. The rollers rotate within the pan to coat the applicator roller.
WO 98/29349 discloses a method and apparatus for applying a sizing composition to glass fibers wherein a moving gathering shoe positioned below the applicator causes the fibers to sweep back and forth along the sizing applicator.
U.S. Pat. No. 3,114,165 to Koteles, et al. discloses a wet film applicator that provides a wet film with a varying thickness.
U.S. Pat. No. 4,476,806 to Lubniewski, et al. discloses an applicator for applying a film of wet material in a preselected, uniform, initial wet film thickness on the top flat surface of a workpiece in a level position.
U.S. Pat. No. 4,869,200 to Euverand discloses a wet film applicator capable of forming films of uniform and non-uniform thicknesses.
It would be advantageous to provide an applicator that can control the thickness of a sizing on an applicator so as to efficiently and effectively coat glass fibers with a sizing composition having high solid content.